This invention relates to anti-blacklash devices, and particularly to anti-backlash nut assemblies for translational movement along a screw in response to relative rotational movement between the nut assembly and screw.
There are many applications in which it is important to drive an element in a machine or apparatus along a screw which provides substantially accurate positional repeatability and constant drag torque control. For example, such a driven element might be used in apparatus for recording, printing, winding, actuating and lifting, or like purposes.
However, should there be an imperfect fit between two members, such as a lead screw and a threaded nut, which are cooperating to transmit movement from one of the members to the other, any resulting slack between the members causes "backlash". If the lead screw is rotated about its longitudinal axis while the nut is prevented from rotating whereby translational movement of the nut longitudinally of the screw is effected, when the direction of rotation of the screw is reversed the direction of movement of the nut is not immediately reversed. This is due to the slack between the cooperating threads of the nut and screw. The slack must be taken up before the nut starts to move in the reverse direction.
This slack or backlash cannot be practically overcome by making a better fit between the screw and nut because this would increase friction and wear with the result that slack soon appears between the members.
Thus, the term "anti-backlash" has been used in the art to designate devices or arrangements which include means for overcoming or reducing the slack between cooperating members, such as a lead screw and a threaded nut, for the purpose of reducing backlash.
Various attempts have been made to provide anti-backlash devices, such as anti-backlash nut assemblies, for overcoming or reducing the slack between lead screws and threaded nuts. Some such prior devices have included employing a compression spring between a pair of axially split nut portions, employing electromagnetic means the energization of which causes relative movement between nut parts so that the slack therebetween is reduced or varied, and providing springs which actually seat in the thread grooves of the lead screw and/or nut themselves. An anti-backlash nut assembly also has been proposed which utilizes an axially and resiliently deformable intermediate section between a pair of nut parts, the deformable intermediate section being rigid in torsion and sheer for axially spreading the nut portions.
The present invention is designed for providing a new and improved anti-backlash nut assembly for overcoming or reducing the slack between cooperating members, such as a lead screw and threaded nut, for the purpose of reducing backlash.